1. Field of the Invention
The present invention relates to a digital picture signal processing apparatus applicable to for example a digital camera apparatus, a method thereof, a digital picture recording apparatus, a method thereof, a transmitting method thereof, and a data record medium thereof.
2. Description of the Related Art
In recent years, a digital picture recording apparatus such as a digital still camera that records an object picture as picture data to a record medium such as a non-volatile semiconductor storage device (for example, a flash memory), a hard disk, or a floppy disk is becoming common. The digital picture recording apparatus converts a photographed object picture into a digital picture signal, compresses the digital picture signal, and records the compressed picture signal information to a record medium. A picture recording apparatus captures a natural picture as a color picture and compresses the captured picture corresponding to the JPEG format.
When a character manuscript, a white board, or the like is photographed, it is preferred to digitize the photographed color picture rather than directly record it as a color picture.
FIG. 1A shows a color picture of a photographed character manuscript. FIG. 1B shows a picture of which a color picture is converted into a digitized picture. As is clear from FIG. 1B, characters and the background of a digitized picture are more clearly distinguished than those of a color picture. Thus, characters can be easily read.
A conventional digital picture recording apparatus superimposes characters on a photographed color picture. However, when the character manuscript is photographed, it is not digitized. When a natural picture other than a character manuscript is photographed, it is preferred to record a color picture.
When a color picture is digitized, it is necessary to distinguish white and black of each pixel of the photographed color picture corresponding to a threshold value. FIG. 1B shows the case that an optimum threshold value is used. If a threshold value is much higher than an optimum threshold value, as shown in FIG. 1C, the entire digitized picture becomes dark. In contrast, when a threshold value is much lower than an optimum threshold value, as shown in FIG. 1D, the entire digitized picture becomes bright, thereby characters become illegible.
In particular, when a picture is photographed by a digital color picture recording apparatus, one of characters and a background picture does not have always a fixed value. Instead, since they can have any value of the color space, a fixed threshold value cannot be pre-designated.
When a picture is recorded by a digital picture recording apparatus, the user may designate the brightness and so forth of the picture. Thus, it is desired to obtain an optimum threshold value regardless of the value of the brightness designated by the user. In addition, when a threshold value is obtained, the value should be accurately and quickly obtained with a limited resource.
For example, when a threshold value is obtained with data of all pixel of a photographed picture, the following problem may take place. When there are a plurality of pictures having different numbers of pixels or sizes, the amount of data to be processed depends on the type of the number of pixels or the type of the size of the picture.
Thus, the time necessary for the threshold value obtaining process varies for each picture. In addition, since the number of pixels varies for each picture, a common threshold value obtaining algorithm cannot be used. In addition, since data of all pixels is used, the process time becomes long. When data of all pixels is used, noise and deterioration contained on the periphery of a picture and information of a peripheral substance adversely affect the threshold value calculating process. Thus, a threshold value cannot be correctly obtained. For example, a peripheral substance other than an object such as a character manuscript or a white board to be digitized may be contained in the picture. Consequently, a threshold value cannot be correctly obtained.